1. Field of the Invention
The present invention pertains generally to measuring and testing devices and more particularly to a device which is capable of synchronizing test pattern generator pulses with a input clock signal from a board under test.
2. Description of the Background
In the process of performing in-circuit testing of components on a printed circuit board, it is often times necessary to produce a series of output signals comprising test pattern pulses from a pattern generator that are sufficient to properly test the component on the printed circuit board. These predetermined test patterns can be produced from a test pattern generator which contains the desired patterns for testing the components. The output of the test pattern generator is normally connected to a series of drivers which produce the desired output pulses for testing the components on the board.
To perform proper testing of the component, it is necessary to synchronize the output signals from the test pattern generator with input clock pulses from there component, i.e., the device under test (DUT). However, in many cases the input clock pulse from the component cannot be disabled because of the nature of the circuit to which the component is connected. Additionally, the output test pattern pulses are normally retarded in phase compared to the input clock pulses produced by the component by up to 100 nanoseconds or more because of inherent delays in the circuitry which is used to generate the output test pattern pulses. This phase difference between the input clock signal and the output signals can result in faulty test readings of the component. Hence, it is desirable to synchronize the output signal of the test pattern generator with the input clock signal from the component that is being tested to ensure that proper test results are obtained. To date, in-circuit board testers have been unable to provide an adequate means for synchronizing these signals.